In recent years, for example, HDMI (High Definition Multimedia Interface) is coming into widespread use as a communications interface for transmitting digital video signals, that is, uncompressed (baseband) video signals (image data), and digital audio signals (audio data) accompanying the video signals, at high speed from DVD (Digital Versatile Disc) recorders, set-top boxes, or other AV sources (Audio Visual sources) to television receivers, projectors, or other displays. For example, Non-Patent Document 1 describes details about the HDMI standard.
FIG. 42 shows an example of the configuration of an AV (Audio Visual) system 10. The AV system 10 has a disc player 11 as a source device, and a television receiver 12 as a sink device. The disc player 11 and the television receiver 12 are connected to each other via an HDMI cable 13. The disc player 11 is provided with an HDMI terminal 11a to which an HDMI transmitting section (HDMI TX) 11b is connected. The television receiver 12 is provided with an HDMI terminal 12a to which an HDMI receiving section (HDMI RX) 12b is connected. One end of the HDMI cable 13 is connected to the HDMI terminal 11a of the disc player 11, and the other end of the HDMI cable is connected to the HDMI terminal 12a of the television receiver 12.
In the AV system 10 shown in FIG. 42, uncompressed image data obtained by being played back on the disc player 11 is transmitted to the television receiver 12 via the HDMI cable 13, and an image based on the image data transmitted from the disc player 11 is displayed on the television receiver 12. Also, uncompressed audio data obtained by being played back on the disc player 11 is transmitted to the television receiver 12 via the HDMI cable 13, and audio based on the audio data transmitted from the disc player 11 is outputted on the television receiver 12.
FIG. 43 shows an example of the configuration of the HDMI transmitting section (HDMI source) 11b of the disc player 11, and the HDMI receiving section (HDMI sink) 12b of the television receiver 12 in the AV system 10 in FIG. 42.
The HDMI transmitting section 11b unidirectionally transmits differential signals corresponding to uncompressed pixel data of one screen's worth of image to the HDMI receiving section 12b on a plurality of channels during an effective image period (hereafter, also referred to as Active Video period as appropriate), which is a period from one vertical sync signal to the next vertical sync signal minus a horizontal blanking period and a vertical blanking period, and also unidirectionally transmits differential signals corresponding to at least audio data and control data accompanying the image, other auxiliary data, or the like to the HDMI receiving section 12b on a plurality of channels during the horizontal blanking period or the vertical blanking period.
That is, the HDMI transmitting section 11b has an HDMI transmitter 81. The transmitter 81 converts uncompressed pixel data of an image into corresponding differential signals, and unidirectionally transmits the differential signals serially to the HDMI receiving section 12b connected via the HDMI cable 13, on a plurality of channels that are three TMDS (Transition Minimized Differential Signaling) channels #0, #1, and #2.
Also, the transmitter 81 converts uncompressed audio data accompanying an image, and further, necessary control data, other auxiliary data, or the like into corresponding differential signals, and unidirectionally transmits the differential signals serially to the HDMI receiving section 12b connected via the HDMI cable 13, on the three TMDS channels #0, #1, and #2.
Further, the transmitter 81 transmits a pixel clock synchronized with pixel data transmitted on the three TMDS channels #0, #1, and #2, to the HDMI receiving section 12b connected via the HDMI cable 13, on a TMDS clock channel. Here, on a single TMDS channel #i (i=0, 1, 2), 10-bit pixel data is transmitted during one clock cycle of the pixel clock.
During an Active Video period, the HDMI receiving section 12b receives differential signals corresponding to pixel data which are unidirectionally transmitted from the HDMI transmitting section 11b on a plurality of channels, and during a horizontal blanking period or a vertical blanking period, receives differential signals corresponding to audio data and control data which are unidirectionally transmitted from the HDMI transmitting section 11b on a plurality of channels.
That is, the HDMI receiving section 12b has an HDMI receiver 82. The receiver 82 receives differential signals corresponding to pixel data and differential signals corresponding to audio data and control data, which are unidirectionally transmitted from the HDMI transmitting section 11b connected via the HDMI cable 13, on the TMDS channels #0, #1, and #2 in synchronization with a pixel clock that is similarly transmitted from the HDMI transmitting section 11b on the TMDS clock channel.
In addition to the three TMDS channels #0 through #2 serving as transmission channels for serially transmitting pixel data and audio data unidirectionally from the HDMI transmitting section 11b to the HDMI receiving section 12b in synchronization with a pixel clock, and the TMDS clock channel serving as a transmission channel for transmitting the pixel clock, transmission channels of an HDMI system formed by the HDMI source transmitting section 11b and the HDMI receiving section 12b include transmission channels called a DDC (Display Data Channel) 83 and a CEC (Consumer Electronics Control) line 84.
The DDC 83 is formed by two unillustrated signal lines included in the HDMI cable 13, and is used for the HDMI transmitting section 11b to read E-EDID (Enhanced Extended Display Identification Data) from the HDMI receiving section 12b that is connected via the HDMI cable 13.
That is, in addition to the HDMI receiver 81, the HDMI receiving section 12b has an EDID ROM (Read Only Memory) that stores E-EDID, which is performance information related to the performance (Configuration/capability) of the HDMI receiving section 12b itself. The HDMI transmitting section 11b reads, via the DDC 83, the E-EDID of the HDMI receiving section 12b from the HDMI receiving section 12b connected via the HDMI cable 13 and, on the basis of this E-EDID, recognizes the performance settings of the HDMI receiving section 12b, that is, for example, image formats (or profiles) supported by an electronic device having the HDMI receiving section 12b, for example, RGB, YCbCr4:4:4, YCbCr4:2:2, and the like.
The CEC line 84 is formed by an unillustrated single signal line included in the HDMI cable 13, and is used for performing bidirectional communication of control data between the HDMI transmitting section 11b and the HDMI receiving section 12b. 
Also, the HDMI cable 13 includes a line (HPD line) 86 that is connected to a pin called HPD (Hot Plug Detect). By using the line 86, a source device can detect the connection of a sink device. Also, the HDMI cable 13 includes a line 87 (power line) that is used to supply power from the source device to the sink device. Further, the HDMI cable 13 includes a reserved line 88.
FIG. 44 shows an example of TMDS transmission data. FIG. 44 shows various periods of transmission data in the case when image data in a horizontal×vertical format of 1920 pixels×1080 lines is transmitted on the three TMDS channels #0, #1, and #2 of HDMI.
During a Video Field in which transmission data is transmitted on the three TMDS channels #0, #1, and #2 of HDMI, three kinds of periods, a Video Data period, a Data Island period, and a Control period exist depending on the kind of transmission data.
Here, the Video Field period is the period from the rising edge (active edge) of a given vertical sync signal to the rising edge of the next vertical sync signal, and is divided into horizontal blanking, vertical blanking, and Active Video that is the period of the Video Field period minus horizontal blanking and vertical blanking.
The Video Data period is allocated to the Active Video period. In this Video Data period, data of 1920 pixels×1080 lines of active pixels constituting one screen's worth of uncompressed image data is transmitted.
The Data Island period and the Control period are allocated to horizontal blanking and vertical blanking. In this Data Island period and Control period, auxiliary data is transmitted. That is, a Data Island period is allocated to a portion of each of horizontal blanking and vertical blanking. In this Data Island period, of the auxiliary data, data not related to control, for example, an audio data packet and the like, is transmitted.
The Control period is allocated to the other portion of each of horizontal blanking and vertical blanking. In this Control period, of the auxiliary data, data related to control, for example, a vertical sync signal and a horizontal sync signal, a control packet, and the like, is transmitted.
FIG. 45 shows an example of packing format when image data (24 bits) is transmitted on the three TMDS channels #0, #1, and #2 of HDMI. Three modes, RGB 4:4:4, YCbCr 4:4:4, and YCbCr 4:2:2, are shown as transmission modes for image data. Here, the relationship between a TMDS clock and a pixel clock is such that TMDS clock=pixel clock.
In the RGB 4:4:4 mode, 8-bit blue (B) data, 8-bit green (G) data, and 8-bit red (R) data are placed in the data areas of individual pixels in the TMDS channels #0, #1, and #2. In the YCbCr 4:4:4 mode, 8-bit blue chrominance (Cb) data, 8-bit luminance (Y) data, and 8-bit red chrominance (Cr) data are placed in the data areas of individual pixels in the TMDS channels #0, #1, and #2.
In the YCbCr 4:2:2 mode, in the data areas of individual pixels in the TMDS channel #0, the data of bit 0 to bit 3 of luminance (Y) data is placed, and also the data of bit 0 to bit 3 of blue chrominance (Cb) data and the data of bit 0 to bit 3 of red chrominance (Cr) data are placed alternately pixel by pixel. Also, in the YCbCr 4:2:2 mode, in the data areas of individual pixels in the TMDS channel #1, the data of bit 4 to bit 11 of luminance (Y) data is placed. Also, in the YCbCr 4:2:2 mode, in the data areas of individual pixels in the TMDS channel #2, the data of bit 4 to bit 11 of blue chrominance (Cb) data and the data of bit 4 to bit 11 of red chrominance (Cr) data are placed alternately pixel by pixel.
FIG. 46 shows an example of packing format when deep color image data (48 bits) is transmitted on the three TMDS channels #0, #1, and #2 of HDMI. Two modes, RGB 4:4:4 and YCbCr 4:4:4, are shown as transmission modes for image data. Here, the relationship between a TMDS clock and a pixel clock is such that TMDS clock=2×pixel clock.
In the RGB 4:4:4 mode, the data of bit 0 to bit 7 and data of bit 8 to bit 15 of 16-bit blue (B) data are placed in the first half and second half of the data area of each pixel in the TMDS channel #0. Also, in the RGB 4:4:4 mode, the data of bit 0 to bit 7 and data of bit 8 to bit 15 of 16-bit green (G) data are placed in the first half and second half of the data area of each pixel in the TMDS channel #1. Also, in the RGB 4:4:4 mode, the data of bit 0 to bit 7 and data of bit 8 to bit 15 of 16-bit red (R) data are placed in the first half and second half of the data area of each pixel in the TMDS channel #2.
Also, in the YCbCr 4:4:4 mode, the data of bit 0 to bit 7 and data of bit 8 to bit 15 of 16-bit blue chrominance (Cb) data are placed in the first half and second half of the data area of each pixel in the TMDS channel #0. Also, in the YCbCr 4:4:4 mode, the data of bit 0 to bit 7 and data of bit 8 to bit 15 of 16-bit luminance (Y) data are placed in the first half and second half of the data area of each pixel in the TMDS channel #1. Also, in the YCbCr 4:4:4 mode, the data of bit 0 to bit 7 and data of bit 8 to bit 15 of 16-bit red chrominance (Cr) data are placed in the first half and second half of the data area of each pixel in the TMDS channel #2.
Since there are no specifications for transmission of stereo image data between HDMI-connected devices which will be put into practice in the coming years, only connections between those of the same manufacture can be realized. In particular, there is no interconnection guarantee for connections with other manufactures' sets. For example, in Patent Document 1, although a proposal is made with regard to the transmission mode for stereo image data and its determination, no proposal is made about transmission via a digital interface such as HDMI. Also, in Patent Document 2, although a proposal is made about the transmission mode for stereo image data using television broadcast radio waves, no proposal is made about transmission via a digital interface.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2003-111101    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2005-6114    Non-Patent Document 1: High-Definition Multimedia Interface Specification Version 1.3a, Nov. 10 2006